Combi vs system boiler and tank

[flameport]

In this configuration, which is more efficient, to have the CH flow from a cylinder or direct from the Combi. ?

If the cylinder is located far away from the tap, and the boiler is close to the tap, and that particular tap is used often, then the combi outlet is better as the hot water will arrive at the tap much quicker and the amount of hot water left in the pipes will be small.

getting the boiler right next to the cylinder might be a bit tight

For that it makes very little difference, because unlike turning a hot tap on briefly many times a day, the cylinder will be heated only once or a few times for an extended period, and the amount of hot water left in the pipes is insignificant compared to the total energy put into the cylinder.

Cylinder location relative to the hot water outlets is far more significant, and all of the pipework should be properly insulated in all cases.

 

[bernardgreen]

Is it not possible that a partially open tap could result in a flow rate adequate to activate the flow sensor but in-adequate to remove all the heat produced by the minimum burn rate.

No

So what does cause a boiler to lock out on over temperature hot water ?

Ignoring the cases of partially open ( or partially blocked ) secondary heat exchanger which result in insufficient flow to remove all the heat

 

[DP]

Boiler does not lock out when water flow is just above minimum for hot water demand. Thermostat is in play to control burner. If the heat is too much, burner goes out.
If there is a tiny trickle running from the boiler, not serving any useful purpose is it.

 

[durhamplumber]

quick job" plumbers started to sell them into houses where they were not the best option.

Bernard,,,why would plumbers go for a quick job when more money in a longer job????..

 

[denso13]

any change in water pressure will alter the flow and hence the temperature of the hot water delivered

I have a thermostatic mixer shower (two in fact off a relatively small combi) which means the temperature doesn't alter at all to a change in water pressure.

 

[bernardgreen]

why would plumbers go for a quick job

The more jobs charged for as "price for the job" they can squeeze into a week the more money they make. This can happen because many customers fall for the line that a combi boiler is better than any system or heat only boiler with cylinder.

 

[Mr.B]

Bernard, I would be more than pleased to know how it is you know so much about how much the vast majority plumbers and heating engineers earn and where you learned all the tricks of the trade that you so generously espouse all the time. I say "the majority" of plumbers and heating engineers as I'm assuming you have some sort of statistical inside knowledge regarding the majority of the UK's plumbing and heating industry operatives - and not a couple of plumbers you read about whilst Googling the topic.

I'd like to think you'd learned all this from a lifetime in the plumbing and heating trade - but when people read about your background (which you've kindly made quite public for all to view) it rather seems you haven't. Quite the opposite, in fact. (unless you regard doing your own plumbing at home as making you a professional, time served heating engineer).

 

[bernardgreen]

Mr B

I never claim to be a professional, time served heating engineer. I do consider my knowledge and experience is adequate to spot the errors, omissions and blatant lies that happen in connection with heating systems. The laws of science cannot be ignored.

your background (which you've kindly made quite public for all to view)

There is far more to my background and experience than will ever be made public on this forum.

 

[Mr.B]

Ah, right. Well that's explained it all then.

(so when you advise people who ask questions here, we can assume it's not on the basis of what you've learned after 20 or 30 years on the job, actually doing the work you know so much about, or at college, studying plumbing, heating and associated subjects and getting qualifications to PROVE that you know what you're on about .... no it's on the basis that you've got the hang of Google and you know a bit about electronics).

 

[bernardgreen]

qualifications to PROVE that you know what you're on about

throughout history many of the best and highly successful engineers had no qualifications at all.

Many "qualifications" prove only that the holder attended a training course for a few days ( or in some cases a few hours )

 

[Mr.B]

Has anyone ever told you you could come across as a bit pompous?

 

[ianmcd]

Has anyone ever told you you could come across as a bit pompous?

You are at the end of the Queue

 

[denso13]

You are always very imprecise with many, often, a number etc etc.

Then marketing people at the manufacturers and "quick job" plumbers started to sell them into houses where they were not the best option.

Which marketing people? Can you back up any of the "quick job" plumbers claim, how often does this actually happen?

The more jobs charged for as "price for the job" they can squeeze into a week the more money they make.

Who is "they"? "Squeeze into a week" shows exactly where you are coming from.

This can happen because many customers fall for the line

How many?

 

[bernardgreen]

Has anyone ever told you you could come across as a bit pompous?

Yes. the important word being could, and for some people I do appear to be pompous. That can be as much their problem ( closed mind ) as it is mine.

How many?

I don't keep a record. But the harm to one seriously disappointed / mislead customer is never balanced out no matter how many satisfied customers the installer can list. It is the harm that gets remembered.

 

[dilalio]

I don't keep a record. But the harm to one seriously disappointed / mislead customer is never balanced out no matter how many satisfied customers the installer can list. It is the harm that gets remembered.

You can't please some people.